Application of Carbon Nanotube/Polymer Composites as Electrode for Polyelectrolyte Membrane Fuel Cells
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Application of Carbon Nanotube/Polymer Composites as Electrode for Polyelectrolyte Membrane Fuel Cells Kirsten Prehn1, Suzana P. Nunes2 and Karl Schulte1 1 Institute of Polymer Composites, Technische Universität Hamburg-Harburg, Denickestrasse 15, 21073 Hamburg, Germany 2 Department of Polymer Technology 1, Institute of Chemistry, GKSS-Forschungszentrum, Max-Planck-Strasse 1, 21502 Geesthacht, Germany ABSTRACT Polyelectrolyte fuel cell membranes (FCMs) consisting of CNTs as electrode and sulfonated polyether ether ketone (SPEEK) were produced by a modified drop casting technique, leading to the formation of an asymmetric structure. Due to the process, the compounded membranes provided a single-sided electron conductivity on account of the CNTs. By using different 3Dstructured CNT-carpets, varying in thickness, density and setup, the properties of the electrode membrane can be adjusted for its designated application. Platinum and ruthenium particles were disposed as catalyst in nano-sized clusters on the CNTs-carpets, which were grown in a chemical vapor deposition (CVD) process. The assemblies and the 3D-nano-structures of the FCMs were analysed by SEM. Furthermore, the surface conductance and the results of the fuel cell tests are described. INTRODUCTION Due to their unique structure, carbon nanotubes (CNTs) possess remarkable mechanical and physical characteristics, in which natural science as well as engineering technology take special interest since several years [1,2]. Depending on the length, diameter and chirality, CNTs are metallic or semiconducting and therefore offer various opportunities for applications in electrical units [3,4]. With respect to the structural features as size, the mentioned electrical, as well as adsorption, mechanical and thermal properties, CNTs lend themself to applications in catalysis [5]. Especially the high electrical conductivity of the CNTs in combination with the structural and chemical properties make this material attractive for an improvement of the performance of electrodes in electrochemical devices, such as polyelectrolyte-membrane fuel cells. The requirements in particular for this application are manifold. Since the electrode is the reaction layer in a fuel cell, the electrolyte, being a proton conductive polymer, has to be combined with catalytic activity and electron conductivity as well as chemical stability against the reactants [6]. Employed as an electrode, CNTs offer prospects to enhance the efficiency of fuel cells due to an improved contact between electrolyte-membrane, electrode and catalyst. Another promising capacity is the large specific surface area of CNTs on which catalyst particles can be distributed in small clusters. This provides an increased catalyst efficiency due to a highly reactive surface area, and thus the amount of catalyst required can be reduced [7,8]. In combination with a good electron conductivity, a CNT based device is a potential alternative for conventional fuel cell electrodes.
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